Brookhaven Lab's John Heiser (left) and Paul Kalb

And Then There’s Mercury Pollution

December 2011 / January 2012 By: Diane Greenberg Volume 9 Number 6

Print this Article

E-mail this Article

Mercury pollution is a serious problem in the U.S. and around the world.  As a neurotoxin, mercury can impair brain development in fetuses and young children and cause neurological damage in adults. Mercury is harmful to ecosystems and wildlife, as it can travel long distances in air to the soil and water bodies and then bioaccumulate as it travels up the food chain, impacting its safety.

According to a 2007 study published by the Mount Sinai School of Medicine’s Center for Children’s Health and the Environment, the U.S. loses $8.7 billion annually because of mercury’s impact on children’s brain development. Mothers of approximately 600,000 newborns each year have mercury in excess of the Environmental Protection Agency’s reference dose and their children may be at higher risk for neurological impacts.  Brookhaven National Laboratory’s In Situ Mercury Remediation (ISMS) process can cost-effectively remove mercury from soil before it has an opportunity to impact human health.

Sources of Mercury

Mercury occurs naturally in the environment. Natural sources of mercury in the atmosphere include volcanoes, geologic deposits and volatilization from the ocean. Rocks, sediments, water and soils naturally contain small amounts of mercury and some mineral deposits and thermal springs contain high concentrations of the element. Also, human activities add a significant amount of mercury to the atmosphere. All coal contains a small amount of mercury and coal-burning power plants generate low concentrations of mercury vapor in their effluent. Collectively, this is the largest source of mercury in the atmosphere introduced by human activity, but because the concentrations are low and the effluent is dispersed widely this source does not create “hot spots” or concentrations at levels that require remediation. 

Laws have been enacted to regulate and reduce mercury air emissions from power plants. Chlor-alkali plants, industrial processes that use mercury, generators of medical and other waste, and mercury, gold and other mineral mining operations are direct sources of mercury pollution, which through poor management of effluents or leakage can lead to mercury concentrations in soil above regulatory limits. This historical industrial use of mercury accounts for widespread pollution. In 2007, the EPA reported that mercury was a “contaminant of concern” at nearly 300 Superfund sites in the U.S.

Current Cleanup Methods

The EPA requires that mercury-contaminated waste be treated to either remove or stabilize the toxic metal and prevent it from leaching into soil or groundwater. Recently, Brookhaven researchers developed ISMS, a method that can treat and remove toxic mercury from soil, sediment, sludge and other industrial waste.

In cases where large areas are contaminated with levels of mercury that are not extremely high, current mercury-extraction methods prove expensive and impractical. One method is excavation, which involves off-site treatment of the mercury-contaminated waste and disposal at an appropriate hazardous waste disposal site, but this method is not the best choice for cleaning up large areas.
“When mercury contaminates a large area, it is too expensive to scoop up and transport for remediation,” said Paul Kalb, Brookhaven Lab’s division head for environmental research and technology and the principal investigator on the project. “This new method can remove mercury without excavating and replacing large volumes of toxic soil or other waste material, reducing both cost and environmental impact.”

Another current method available for mercury remediation is thermal desorption. In this method, soil is heated, and the mercury is vaporized. A gas or vacuum system then transports the vaporized mercury and water to an air-emission treatment system.

The thermal desorption process also has limitations, Kalb said. “Besides using a lot of energy for heat—an expensive process—there are environmental concerns. For example, air emissions of metals and other potentially toxic substances during vaporization and leaching mercury from stockpiled soil into water are potential problem areas. In contrast, the Brookhaven process can treat and remove mercury contamination from the ground in an environmentally sound manner.”

ISMS: A “Chemical Magnet”

In the new process, mercury is drawn to specially designed treatment rods that contain a sulfur-based reagent. When a series of rods is placed in mercury-contaminated soil or other waste material, the mercury migrates by diffusion to the rods and reacts with the sulfur reagent to form a mercury sulfide compound. The resulting concentration gradient enhances the transport of mercury vapor toward the treatment rod.  The rod, which contains the stable, insoluble compound, can then be removed for safe disposal at a hazardous waste facility without having to dig up large volumes of soil or waste material.
 “Using x-ray fluorescence, we initially tested samples of mercury-contaminated sand in an area about three inches in diameter before and after exposure to the treatment rod,” Kalb said. “After 50 days, the mercury concentration in the sand was 42 times lower than at the start of the test. Repeat testing at slightly larger laboratory-scales confirmed the feasibility of the process. We believe we can eventually develop the technology to a point where we can effectively remediate a very large area of mercury contamination.”

While these bench-scale, proof-of-principle studies were very successful, additional R&D for further scale-up and a better understanding of performance under field conditions is needed before the technology is deployed and commercially offered. Brookhaven Lab is now seeking collaborations with industry and others in the DOE complex to accomplish this next task before commercialization.

Benefits in the Billions?

Since mercury contamination is widespread throughout the world, the potential market for the ISMS remediation technology is worth hundreds of millions to tens of billions of dollars in potential economic activity and benefits. ISMS would be useful for remediation in numerous industrial sites around the world, including those that use the chlor-alkali process, important for making substances for manufacturing chemicals, soap, glass and paper, among numerous other products. Also, mercury is used in the production of fluorescent lights, thermometers, batteries and electrical switches, all in amounts that may necessitate cleanup.

For information about collaboration and partnership with Brookhaven Lab to further develop the technology in a pilot field study or to license ISMS, please contact Steven Wood with Brookhaven National Laboratory’s Office of Technology Commercialization and Partnerships, at (631) 344-3450, or swood@bnl.gov.

Diane Greenberg is a writer at Brookhaven National Laboratory.